Thin film batteries are used to supply energy in applications requiring a small size, high specific energy or density, or resistance to environmental degradation. Common applications include, for example, portable electronics, medical devices, and outer space systems. A thin film battery typically comprises a substrate that supports a stack of thin films that can include one or more of a current collector, cathode, anode and electrolyte, the thin films typically having a thickness of less than 100 microns. The thin films can be formed on the substrate by conventional fabrication processes, such as for example, physical or chemical vapor deposition (PVD or CVD), oxidation, nitridation, electron beam evaporation, and electroplating processes.
A lithium ion, thin film battery typically includes a cathode of a lithium-based material such as LiCoOx, and in these batteries, increasing the thickness of this cathode film increases the energy density of the battery. The thicker cathode film provides greater charge retention and faster charging and discharging rates. For example, specific energy levels of at least 250 Whr/L can be achieved using a cathode film having a thickness of 5 microns or higher, as for example is taught in commonly assigned U.S. patent application Ser. No. 11/007,362 entitled “THIN FILM BATTERY AND METHOD OF MANUFACTURE” which is incorporated by reference herein, and in its entirety. The cathode film can be deposited as an amorphous or microcrystalline film in a single pass deposition process, and thereafter, crystallized by heating the film; or deposited in a sequence of thin films to form a thicker cathode comprising a stack of films.
However, conventional sputtering processes have several limitations, which include relatively slow cathode film deposition rates that make it economically difficult to manufacture thick cathode films. For example, conventional radio frequency magnetron sputtering processes often result in deposition rates of around 0.2 microns per hour. Increasing the sputter deposition rates can result in plasma arcing which affects the quality of deposited films. These processes also require an impedance matching network to match the impedance of magnetron and power supply to increase plasma stability and efficiency. However, it is also often difficult to identify the correct impedance matching parameters.
Thus it is desirable to have a process for depositing relatively thick cathode films in a short time to provide a battery having relatively higher energy density or specific energy. There is also a need for depositing such cathode films with decreased electrical contact resistances while still maintaining good deposition rates. There is further a need for depositing lithium cobalt oxide without arcing or impedance matching problems.